Tyre with low rolling resistance, tread band and elastomeric composition used therein

ABSTRACT

An elastomeric composition includes at least one diene elastomeric polymer, at least one reinforcing filler including silica, at least one silica coupling agent including at least one hydrolyzable silane group, and titanium dioxide. A weight ratio of the at least one silica coupling agent to the titanium dioxide is greater than or equal to 0.5:1. Also disclosed is a tyre, tread band, and cross-linked elastomeric manufactured article including the elastomeric composition. The tyre includes at least one element of cross-linked elastomeric material including the elastomeric composition. The tread band may be that at least one element.

The present invention relates to a tyre for vehicle wheels, to a treadband and to a cross-linkable elastomeric composition.

More particularly, the present invention relates to a tyre for vehiclewheels comprising at least one element of cross-linked elastomericmaterial including at least one reinforcing filler comprising silica, atleast one silica coupling agent and titanium dioxide.

The present invention also relates to a tread band including across-linkable elastomeric composition comprising at least onereinforcing filler including silica, at least one silica coupling agentand titanium dioxide, as well as an elastomeric composition comprisingat least one reinforcing filler including silica, at least one silicacoupling agent and titanium dioxide.

In the rubber industry, in particular in the industry for production ofvehicle wheel tyres, use of elastomeric compositions is known in whichreinforcing fillers are incorporated into the polymeric base for thepurpose of improving the features of the cross-linked manufacturedarticle, in particular mechanical properties and resistance to abrasion.Due to its high reinforcing power, carbon black is the most widely usedreinforcing filler. However, carbon black gives the cross-linkedmanufactured article marked hysteresis features, i.e. an increase in theheat dissipated under dynamic conditions which, as known, in the case ofa tyre, gives rise to an increase of the rolling resistance of the tyreitself. This brings about an increase in the vehicle fuel consumptionand, consequently, an increase both in the locomotion costs and in airpollution. An attempt to reduce these negative effects can be made byusing smaller amounts of carbon black and/or a carbon black having areduced surface area. This however, inevitably brings to a reduction inthe reinforcing action, which will worsen the mechanical properties andthe abrasion resistance of the finished product.

For the purpose of reducing the hysteresis features of cross-linkedmanufactured articles, use of the so-called “white” reinforcing fillersis known, such as gypsum, talc, kaolin, bentonite, titanium dioxide,silicates of various types and, above all, silica which can fully orpartly replace carbon black. In this connection, reference can be madeto European Patent EP 501,227, for example.

As above stated, among the so-called “white” fillers use of titaniumdioxide is also known, in addition to silica.

With reference to this, the Japanese Patent Application JP 2000/38477discloses an elastomeric composition to be used for manufacture of tyretread bands, comprising a blend including 10 to 50 parts by weight oftitanium dioxide and 30 to 90 parts by weight of silica based on 100parts by weight of a diene elastomeric polymer, and a coupling agent inan amount of between 5% and 15% with respect to silica. The couplingagent can be selected from sulphur-containing organosilane compoundssuch as bis(3-triethoxysilylpropyl)tetrasulphide,3-mercapto-propyltrimethoxysilane, 2-mercaptoethyl-trimethoxysilane, forexample. Said composition would be provided with good Mooney viscosityand would enable tread bands provided with a better resistance to wearto be obtained.

Use of said reinforcing fillers, in particular silica, involves a seriesof drawbacks, substantially correlated with the weak affinity of saidfillers for the elastomeric polymers commonly used in tyre production.In particular, in order to enable silica to have a good dispersiondegree in the polymeric base the elastomeric compositions are requiredto be submitted to a prolonged thermomechanical mixing action. Inaddition, silica particles that have a strong tendency to coalesce evenwhen finely dispersed in a polymeric base, adversely affect storagestability of the unvulcanized elastomeric compositions formingagglomerates, and thus causing a great increase in viscosity. Finally,the acid groups present in silica can cause strong interactions with thebasic substances usually present in the elastomeric compositions such asvulcanization accelerators for example, thereby reducing cross-linkingdegree and velocity.

To increase affinity of silica for the elastomeric matrix, appropriatecoupling agents are currently used such as sulphur-containingorganosilane products for example, which have two different groups: afirst group which is able to interact with the silanol groups present onthe silica surface, a second group able to promote interaction with thesulphur-vulcanizable elastomeric polymers. Use of said coupling agentshowever, limits the maximum temperature that can be achieved during themixing and thermomechanical-working operations of the elastomericcomposition, under penalty of an irreversible thermal degradation of thecoupling agent. In addition, the high cost of said coupling agentsadversely affects the cost of the finished product.

For the purpose of overcoming the above drawbacks, in the known artintroduction of other compounds able to promote silica reaction with thecoupling agent thereby improving interaction thereof with theelastomeric polymers has been suggested.

For instance, the European Patent Application EP 801,112 discloseselastomeric compositions comprising silica, a silane as the couplingagent and/or a polysiloxane having alkoxysilyl groups in the molecule, acondensation catalyst in an amount of between 0.5% and 200% by weightwith respect to said coupling agent and/or to said polysiloxane. Saidcondensation catalyst can be selected from metal carboxylates such astetraisopropyl titanate, dibutyl tin dilaurate, zinc octylate, forexample; or from amines such as dimethyl stearylamine, etc., forexample. Addition of the coupling agent and/or polysiloxane and thecondensation catalyst to said elastomeric compositions would enablereaction between silica and the coupling agent and/or polysiloxane to beaccelerated and, consequently, the physical properties of saidelastomeric compositions to be improved, in particular stress at tensiledeformation, wear resistance, tandelta and other physical properties.

Patent application EP 1,031,604 describes an elastomer compositioncomprising (a) 100 parts by weight of an elastomer containing anolefinic unsaturation, which is selected from conjugated dienehomopolymers and copolymers and from copolymers of at least oneconjugated diene with an aromatic vinyl compound; (a) 10 to 150 phr ofsilica; (c) 0.1 to 15 phr of a sulphur-containing organosilane compound;(d) 0.1 to 10 phr of a tin carboxylate. Said tin carboxylate (forexample tin octanoate) would be able to give the elastomer compositionsimproved both mechanical and dynamic properties, better abrasionresistance as well as less rolling resistance.

The Applicant has now found that titanium dioxide added to elastomercompositions including silica and a silica coupling agent, is able topromote the silanization reaction (increase in yield) and therefore, toenable, if required, a reduction in the amount of said coupling agent.In addition, titanium dioxide is able to improve the static mechanicalproperties (in particular is able to give a better reinforcing effect),the dynamic mechanical properties (in particular tandelta to hightemperatures) and the abrasion resistance of said elastomericcompositions. Also the viscosity values and the rheometric properties ofsaid elastomeric compositions keep within acceptable values, in this wayensuring a good processing and extrusion capability.

Accordingly, in a first aspect the present invention relates to a tyrefor vehicle wheels comprising at least one element of cross-linkedelastomeric material, in which said element includes an elastomericcomposition comprising:

-   -   (a) at least one diene elastomeric polymer;    -   (b) at least one silica-including reinforcing filler;    -   (c) at least one silica coupling agent containing at least one        hydrolyzable silane group;    -   (d) titanium dioxide; wherein the weight ratio between said        coupling agent (c) and titanium dioxide (d) is not less than        0.5, preferably comprised between 2 and 6.

According to a preferred embodiment, the present invention relates to atyre for vehicle wheels comprising:

-   -   a carcass structure with at least one carcass ply shaped in a        substantially toroidal configuration, the opposite lateral edges        of which are associated with respective right-hand and left-hand        bead wires, each bead wire being enclosed in a respective bead;    -   a belt structure comprising at least one belt strip applied in a        circumferentially external position relative to said carcass        structure;    -   a tread band superimposed circumferentially on said belt        structure;    -   a pair of side walls applied laterally on opposite sides        relative to said carcass structure;        wherein said element which includes said elastomeric composition        is the tread band.

In another aspect, the present invention relates to a tread band forvehicle wheel tyres including a cross-linkable elastomeric compositioncomprising:

-   -   (a) at least one diene elastomeric polymer;    -   (b) at least one silica-including reinforcing filler;    -   (c) at least one silica coupling agent containing at least one        hydrolyzable silane group;    -   (d) titanium dioxide; wherein the weight ratio between said        coupling agent (c) and titanium dioxide (d) is not less than        0.5, preferably comprised between 2 and 6.

In a further aspect, the present invention relates to an elastomericcomposition comprising:

-   -   (a) at least one diene elastomeric polymer;    -   (b) at least one silica-including reinforcing filler;    -   (c) at least one silica coupling agent containing at least one        hydrolyzable silane group;    -   (d) titanium dioxide; wherein the weight ratio between said        coupling agent (c) and titanium dioxide (d) is not less than        0.5, preferably comprised between 2 and 6.

In a still further aspect, the present invention relates to across-linked elastomeric manufactured article obtained by cross-linkingan elastomeric composition comprising:

-   -   (a) at least one diene elastomeric polymer;    -   (b) at least one silica-including reinforcing filler;    -   (c) at least one silica coupling agent containing at least one        hydrolyzable silane group;    -   (d) titanium dioxide; wherein the weight ratio between said        coupling agent (c) and titanium dioxide (d) is not less than        0.5, preferably comprised between 2 and 6.

In a preferred embodiment, the diene elastomeric polymer (a) to be usedin accordance with the present invention can be selected from thosecurrently employed in sulphur cross-linkable elastomeric compositions,particularly suitable for tyre manufacture, i.e. among unsaturated-chainelastomeric polymers or copolymers having a glass transition temperature(T_(g)) generally lower than 20° C., preferably comprised between 0° C.and −90° C. These polymers and copolymers can be of natural origin orthey can be obtained by solution polymerization, emulsionpolymerization, or gas-phase polymerization of one or more conjugateddiolefins, possibly mixed with at least one co-monomer selected frommonovinylarenes and/or polar co-monomers in amounts not higher than 60%by weight.

Conjugated diolefins generally have from 4 to 12, preferably from 4 to8, carbon atoms and can be selected for example from the groupcomprising: 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 1,3-hexadiene, 3-buthyl-1,3-octadiene,2-phenyl-1,3-butadiene and mixtures thereof. Particularly preferred are1,3-butadiene and isoprene.

Monovinylarenes possibly usable as co-monomers generally have from 8 to20, preferably from 8 to 12 carbon atoms, and can be selected from, forexample: styrene; 1-vinylnaphthalene; 2-vinylnaphthalene; some alkyl,cycloalkyl, aryl, akylaryl or arylalkyl derivatives of styrene such as,for example, α-methylstyrene, 3-methylstyrene, 4-propylstyrene,4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene,4-p-tolylstyrene, 4-(4-phenylbutyl)styrene, or mixtures thereof.Particularly preferred is styrene.

Polar co-monomers possibly usable can be, for example, selected from:vinylpyridines, vinylquinolines, acryl and alkylacryl acid esters,nitriles, or mixtures thereof such as, for example, methylacrylate,ethylacrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile,or mixtures thereof.

Preferably, the diene elastomeric polymer (a) usable in the presentinvention can be for example selected from: cis-1,4-polyisoprene(natural or synthetic, preferably natural rubber), 3,4-polyisoprene,polybutadiene (in particular high “1,4-cis” polybutadiene), possiblyhalogenated isoprene/isobutene copolymers, 1,3-butadiene/acrylonitrilecopolymers, styrene/1,3-butadiene copolymers,styrene/isoprene/1,3-butadiene copolymers,styrene/1,3-butadiene/acrylonitrile copolymers, or mixtures thereof.

The elastomeric composition in accordance with the present invention canpossibly comprise at least one elastomeric polymer of at least onemonoolefin with at least one olefinic co-monomer or derivatives thereof(e). Monoolefins can be selected from: ethylene and α-olefins generallyhaving from 3 to 12 carbon atoms, such as, for example, propylene,1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof. Preferredare: copolymers of ethylene and an α-olefin, and possibly a diene;homopolymers of isobutene or copolymers thereof with smaller amounts ofa diene, possibly at least partly halogenated. The possibly presentdiene generally has from 4 to 20 carbon atoms and is preferably selectedfrom: 1,3-butadiene, isoprene, 1,4-hexadiene, 1,4-cyclohexadiene,5-ethylidyne-2-norbornene, 5-methylidyne-2-norbornene,5-vinyl-2-norbornene, or mixtures thereof. Of them particularlypreferred are: ethylene/propylene (EPR) copolymers orethylene/propylene/diene (EPDM) copolymers; polyisobutene; butylrubbers; halobutyl rubbers, in particular chlorobutyl or bromobutylrubbers; or mixtures thereof.

Also used can be a diene elastomeric polymer (a) or an elastomericpolymer (e) functionalized by reaction with suitable terminating orcoupling agents. In particular, diene elastomeric polymers obtained byanionic polymerization in the presence of an organometallic initiator(in particular an organolithium initiator) can be functionalized byreaction of the residual organometallic groups derived from theinitiator with suitable terminating or coupling agents such as, forexample, imines, carbodiimides, alkyltin halides, substitutedbenzophenones, alkoxy- or aryloxy-silanes (see, for example, EuropeanPatent EP 451,604 or U.S. Pat. Nos. 4,742,124 and 4,550,142).

The elastomeric composition in accordance with the present invention maypossibly comprise at least one thermoplastic polymer having a mainhydrocarbon chain to which hydrophilic groups are bonded (f). Thepreferred ones are polyacrylic acid, polymethacrylic acid,polyhydroxyalkylalkylate, polyalkylacrylate, polyacrylamide,acrylamide/acrylic acid copolymers, polyvinyl alcohol, polyvinylacetate, vinylalcohol/vinylacetate copolymers, ethylene/vinylacetatecopolymers, ethylene/vinylalcohol copolymers,ethylene/vinylalcohol/vinylacetate terpolymers, polyvinylsulfonic acid,polystyrene sulfonate, or mixtures thereof. For a more detaileddescription of said thermoplastic polymer (f) reference can be made forexample, to the Patent Application Wo 01/49785 in the name of the sameApplicant.

According to a preferred embodiment, the silica-including reinforcingfiller (b) can generally be a pyrogenic silica or preferably aprecipitated silica, having a BET surface area (measured according toISO standard 5794/1) comprised between 50 m²/g and 500 m²/g, preferablybetween 70 m²/g and 200 m²/g.

The silica-including reinforcing filler (b) is present in theelastomeric composition in an amount preferably comprised between 0.1phr and 120 phr, more preferably between 10 phr and 90 phr.

For the purposes of the present description and of the claims, the term“phr” means the parts by weight of a given component of the elastomericcomposition per 100 parts by weight of elastomeric base.

The elastomeric composition in accordance with the present invention maypossibly include a further reinforcing filler that can be for exampleselected from: carbon black, alumina, aluminosilicates, calciumcarbonate, kaolin, or mixtures thereof.

The carbon black types to be used in accordance with the presentinvention can be selected from those conventionally used in tyremanufacture, generally having a surface area of not less than 20 m²/g(determined by CTAB absorption as described in ISO standard 6810).

According to a preferred embodiment, the silica coupling agentcontaining at least one hydrolysable silane group (c) also contains atleast one sulphur atom. Preferably said coupling agent can be selectedfrom the compounds of formula (I):Z-Alk-S_(n)-Alk-Z  (I)wherein Z is selected from the following groups: —Si(R₁)₂(R₂),—Si(R₁)(R₂)₂, and —Si(R₂)₃, wherein R₁ is a C₁-C₄ alkyl group, acyclohexyl or a phenyl group and R₂ is a C₁-C₈ alkoxy group, or a C₅-C₈cycloalkoxy group; Alk is a divalent hydrocarbon group having from 1 to18 carbon atoms, and n is a number included between 2 and 8.

Specific examples of compounds of formula (I) to be used in accordancewith the present invention are:

-   3,3′-bis(trimethoxysilylpropyl)disulfide,-   3,3′-bis(triethoxysilylpropyl)disulfide,-   3,3′-bis(triethoxysilylpropyl)tetrasulfide,-   3,3′-bis(tri-etoxysilylpropyl)octasulfide,-   3,3′-bis(trimethoxysilylpropyl)tetrasulfide,-   2,2′bis(triethoxysilylethyl)tetrasulfide,-   3,3′-bis(trimethoxysilylpropyl)trisulfide,-   3,3′-bis(triethoxysilylpropyl)trisulfide-   3,3′-bis(tributoxysilylpropyl)disulfide,-   3,3′-bis(trimethoxysilylpropyl)hexasulfide,-   3,3′-bis(trimethoxysilylpropyl)octasulfide,-   3,3′-bis(trioctoxysilylpropyl)tetrasulfide,-   3,3′-bis-(trihexoxysilylpropyl)disulfide,-   3,3′-bis(tri-2-ethylhexoxysilylpropyl)trisulfide,-   3,3′-bis(triisooctoxylsilylpropyl)tetrasulfide,-   3,3′-bis(tri-t-butoxysilylpropyl)disulfide,-   2,2′-bis(methoxydiethoxysilylethyl)tetrasulfide,-   2,2′-bis(tripropoxysilylethyl)pentasulfide,-   3,3′-bis(tricyclohexoxysilylpropyl)tetrasulfide,-   3,3′-bis(tricyclopentoxysilylpropyl)trisulfide,-   2,2′-bis(tri-2-methylcyclohexoxysilylethyl)tetrasulfide,-   bis(trimethoxysilylmethyl)tetrasulfide,-   3-methoxyethoxypropoxysilyl-3′-diethoxybutoxysilylpropyltetrasulfide,-   2,2′-bis(dimethylmethoxysilylethyl)disulfide,-   2,2′-bis-(dimethyl-s-butoxysilylethyl)trisulfide,-   3,3′-bis(methylbutylethoxysilylpropyl)tetrasulfide,-   3,3′-bis(di-t-butylmethoxysilylpropyl)tetrasulfide,-   2,2′-bis(phenylmethylmethoxysilylethyl)trisulfide,-   3,3′-bis(diphenylisopropoxysilylpropyl)tetrasulfide,-   3,3′-bis(diphenylciclohexoxysilylpropyl)disulfide,-   3,3′-bis(dimethylethylmercaptosilylpropyl)tetrasulfide,-   2,2′-bis(methyldimethoxysilylethyl)trisulfide,-   2,2′-bis(methylethoxypropoxysilylethyl)tetrasulfide,-   3,3′-bis(diethylmethoxysilylpropyl)tetrasulfide,-   3,3′-bis(ethyl-di-s-butoxysilylpropyl)disulfide,-   3,3′-bis(propyldiethoxysilylpropyl)disulfide,-   3,3′-bis(buthyldimethoxysilylpropyl)trisulfide,-   3,3′-bis(phenyldimethoxysilylpropyl)tetrasulfide,-   3-phenylethoxybutoxysilyl-3′-trimethoxysilylpropyltetrasulfide,-   4,4′bis(trimethoxysilylbutyl)tetrasulfide,-   6,6′-bis(triethoxysilylhexyl)tetrasulfide,-   12,12′-bis(triisopropoxysilyldodecyl)disulfide,-   18,18′-bis(trimethoxysilyloctadecyl)tetrasulfide,-   18,18′-bis(tripropoxysisilyloctadecenyl)tetrasulfide,-   4,4′-bis(trimethoxysilylbuten-2-yl)tetrasulfide,-   4,4′bis(trimethoxysilylcyclohexylene)tetrasulfide,-   5,5′-bis(dimethoxymethylsilylpentyl)trisulfide,-   3,3′-bis(trimethoxysilyl-2-methylpropyl)tetrasulfide,-   3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide.

Preferred coupling agents are3,3-bis(3-triethoxysilylpropyl)tetrasulfide andbis(3-triethoxysilylpropyl)disulfide. Said coupling agents can be usedas such or in a suitable mixture with an inert filler (carbon black, forexample) so as to facilitate incorporation of same into the elastomericcomposition.

The coupling agent (c) is present in the elastomeric composition in anamount preferably comprised between 1 phr and 15 phr, more preferablybetween 1.5 phr and 10 phr.

According to a preferred embodiment, the titanium dioxide (d) can beselected from those having the following characteristics:

-   -   purity: not less than 85%, preferably greater than 98%;    -   NSA surface area (measured by surface absorption of nitrogen        according to ISO standard 5794/1): comprised between 5 m²/g and        200 m²/g, preferably between 8 m²/g and 100 m²/g;    -   average particle diameter comprised between 10 nm and 400 nm,        preferably between 20 nm and 200 nm.

It should be pointed out that, for the purposes of the presentdescription and of the following claims, by the term “titanium dioxide”it is intended compounds of formula TiO₂ as well as their hydratedforms, both crystalline and amorphous forms, in particular thecrystalline form of said titanium dioxide (rutile, anatase, or a mixtureof said crystalline varieties, for example).

Possibly used may also be a titanium dioxide coated with organiccoatings (polyols, for example) or inorganic coatings (alumina, silica,for example).

Said titanium dioxide can be either used as such or it can be mixed withthe silica coupling agent before addition to the elastomericcomposition.

The titanium dioxide (d) is present in the elastomeric composition in anamount preferably comprised between 0.2 phr and 5 phr, more preferablybetween 0.5 phr and 3 phr.

The elastomeric composition in accordance with the present invention canbe vulcanized following known techniques, in particular usingsulphur-based vulcanization systems usually employed for dieneelastomeric polymers. For the purpose, in the composition after athermomechanical working step, a sulphur-based vulcanizing agent isincorporated together with vulcanization accelerators. During thelast-mentioned working step, temperature is generally maintained below120° C., preferably below 100° C., so as to avoid undesirablepre-cross-linking phenomena.

The vulcanizing agent most advantageously used is sulphur, or moleculescontaining sulphur (sulphur donors), with accelerators and activatorsknown to those skilled in the art.

Activators of particular efficiency are zinc compounds and, inparticular, ZnO, ZnCO₃, zinc salts of saturated or unsaturated fattyacids, having from 8 to 18 carbon atoms such as zinc stearate forexample, preferably formed in situ in the elastomeric compositionstarting from ZnO and a fatty acid, as well as BiO, PbO, Pb₃O₄, PbO₂, ormixtures thereof.

Accelerators of common use can be selected from ditiocarbamates,guanidines, thioureas, thiazoles, sulfenamides, thiourames, amines,xanthates, or mixtures thereof.

The elastomeric composition in accordance with the present invention mayfurther comprise other additives of common use selected on the basis ofthe specific intended application. For instance, added to saidcomposition may be: antioxidants, anti-ageing agents, plasticizers,adhesives, anti-ozone agents, modifying resins, fibres (Kevlar® pulp,for example), or mixtures thereof.

In particular, for the purpose of further improving processability, aplasticizer can be added to the elastomer composition in accordance withthe present invention, which is generally selected from mineral oils,vegetable oils, synthetic oils, or mixtures thereof such as, aromaticoil, naphthenic oil, phthalates, soybean oil, or mixtures thereof. Theplasticizer amount can generally range between 2 phr and 100 phr,preferably between 5 phr and 50 phr.

Preparation of the elastomeric composition in accordance with thepresent invention can be accomplished by mixing the polymeric componentswith the reinforcing filler, the coupling agent and titanium dioxidewith the other additives following known techniques. The mixing may becarried out, for example, using an open mixer of open-mill type, or aninternal mixer of the type with tangential rotors (Banbury) or withinterlocking rotors (Intermix), or in continuous mixers of Ko-Kneadertype (Buss) or of co-rotating or counter-rotating twin-screw type.

The present invention will be now further illustrated with the aid ofsome examples, reference being made to the enclosed FIG. 1 representinga sectional view of a portion of a tyre made in accordance with theinvention.

Denoted at “a” is an axial direction, at “r” a radial direction. Forsimplicity, FIG. 1 only represents a portion of the tyre, the remainingportion not shown being identical to, and disposed in symmetry with theradial direction “r”.

The tyre (100) comprises at least one carcass ply (101), the oppositelateral edges of which are associated with respective bead wires (102).The association between the carcass ply (101) and the bead wires (102)is achieved here by folding back the opposite lateral edges of thecarcass ply (101) around the bead wires (102) so as to form theso-called carcass back-folds (110 a) as shown in FIG. 1.

Alternatively, the conventional bead wires (102) can be replaced with apair of circumferentially inextensible annular inserts formed fromelongate components arranged in concentric coils (not represented inFIG. 1) (see, for example, European patent applications EP 928,680 andEP 928,702). In this case, the carcass ply (101) is not back-foldedaround said annular inserts, the coupling being provided by a secondcarcass ply (not represented in FIG. 1) applied externally over thefirst.

The carcass ply (101) generally consists of a plurality of reinforcingcords arranged parallel to each other and at least partially coated witha layer of elastomeric compound. These reinforcing cords are usuallymade of textile fibres, for example rayon, nylon or polyethyleneterephthalate, or of steel wires stranded together, coated with a metalalloy (for example copper/zinc, zinc/manganese, zinc/molybdenum/cobaltalloys and the like).

The carcass ply (101) is usually of radial type, i.e. it incorporatesreinforcing cords arranged in a substantially perpendicular directionrelative to a circumferential direction. Each bead wire (102) isenclosed in a bead (103), defined along an inner circumferential edge ofthe tyre (100), with which the tyre engages on a rim (not represented inFIG. 1) forming part of a vehicle wheel. The space defined by eachcarcass back-fold (101 a) contains a bead filler (104) in which the beadwires (102) are embedded. An antiabrasive strip (105) is usually placedin an axially external position relative to the carcass back-fold (101a).

A belt structure (106) is applied along the circumference of therubberized carcass ply (101). In the particular embodiment in FIG. 1,the belt structure (106) comprises two belt strips (106 a, 106 b) whichincorporate a plurality of reinforcing cords, typically metal cords,which are parallel to each other in each strip and intersecting withrespect to the adjacent strip, oriented so as to form a predeterminedangle relative to a circumferential direction. On the radially outermostbelt strip (106 b) may optionally be applied at least one zero-degreereinforcing layer (106 c), commonly known as a “0° belt”, whichgenerally incorporates a plurality of reinforcing cords, typicallytextile cords, arranged at an angle of a few degrees relative to acircumferential direction, and coated and welded together by means of anelastomeric material.

A side wall (108) is also applied externally onto the rubberized carcassply (101), this side wall extending, in an axially external position,from the bead (103) to the end of the belt structure (106).

A tread band (109), whose lateral edges are connected to the side walls(108), is applied circumferentially in a position radially external tothe belt structure (106). Externally, the tread band (109), which can beproduced according to the present invention, has a rolling surface (109a) designed to come into contact with the ground. Circumferentialgrooves which are connected by transverse notches (not represented inFIG. 1) so as to define a plurality of blocks of various shapes andsizes distributed over the rolling surface (109 a) are generally made inthis surface (109 a), which is represented for simplicity in FIG. 1 asbeing smooth.

A strip made of elastomeric material (110), commonly known as a“mini-side wall”, may optionally be present in the connecting zonebetween the side walls (108) and the tread band (109), this mini-sidewall generally being obtained by co-extrusion with the tread band andallowing an improvement in the mechanical interaction between the treadband (109) and the side walls (108). Alternatively, the end portion ofthe side wall (108) directly covers the lateral edge of the tread band(109). A underlayer which forms, with the tread band (109), a structurecommonly known as a “cap and base” (not represented in FIG. 1) mayoptionally be placed between the belt structure (106) and the tread band(109).

A layer of elastomeric material (111) which serves as an “attachmentsheet”, i.e. a sheet capable of providing the connection between thetread band (109) and the belt structure (106), may be placed between thetread band (109) and the belt structure (106).

In the case of tubeless tyres, a rubber layer (112) generally known as a“liner”, which provides the necessary impermeability to the inflationair of the tyre, may also be provided in a radially internal positionrelative to the rubberized carcass ply (101).

The process for producing the tyre according to the present inventioncan be carried out according to techniques and using apparatus that areknown in the art, as described, for example, in patents EP 199 064, U.S.Pat. No. 4,872,822, U.S. Pat. No. 4,768,937, said process including atleast one stage of manufacturing the green tyre and at least one stageof vulcanizing this tyre.

More particularly, the process for producing the tyre comprises thestages of preparing, beforehand and separately from each other, a seriesof semi-finished products corresponding to the various parts of the tyre(carcass plies, belt structure, bead wires, fillers, side walls andtread band) which are then combined together using a suitablemanufacturing machine. Next, the subsequent vulcanization stage weldsthe abovementioned semi-finished products together to give a monolithicblock, i.e. the finished tyre.

Naturally, the stage of preparing the above-mentioned semi-finishedproducts will be preceded by a stage of preparing and moulding thevarious blends, of which said semi-finished products are made, accordingto conventional techniques.

The green tyre thus obtained is then passed to the subsequent stages ofmoulding and vulcanization. To this end, a vulcanization mould is usedwhich is designed to receive the tyre being processed inside a mouldingcavity having walls which are countermoulded to define the outer surfaceof the tyre when the vulcanization is complete.

Alternative processes for producing a tyre or parts of a tyre withoutusing semi-finished products are disclosed, for example, in theabovementioned patent applications EP 928,680 and EP 928,702.

The green tyre can be moulded by introducing a pressurized fluid intothe space defined by the inner surface of the tyre, so as to press theouter surface of the green tyre against the walls of the mouldingcavity. In one of the moulding methods widely practised, a vulcanizationchamber made of elastomeric material, filled with steam and/or anotherfluid under pressure, is inflated inside the tyre closed inside themoulding cavity. In this way, the green tyre is pushed against the innerwalls of the moulding cavity, thus obtaining the desired moulding.Alternatively, the moulding can be carried out without an inflatablevulcanization chamber, by providing inside the tyre a toroidal metalsupport shaped according to the configuration of the inner surface ofthe tyre to be obtained as decribed, for example, in patent EP 242,840.The difference in coefficient of thermal expansion between the toroidalmetal support and the crude elastomeric material is exploited to achievean adequate moulding pressure.

At this point, the stage of vulcanizing the crude elastomeric materialpresent in the tyre is carried out. To this end, the outer wall of thevulcanization mould is placed in contact with a heating fluid (generallysteam) such that the outer wall reaches a maximum temperature generallyof between 100° C. and 230° C. Simultaneously, the inner surface of thetyre is heated to the vulcanization temperature using the samepressurized fluid used to press the tyre against the walls of themoulding cavity, heated to a maximum temperature of between 100° C. and250° C. The time required to obtain a satisfactory degree ofvulcanization throughout the mass of the elastomeric material can varyin general between 3 min and 90 min and depends mainly on the dimensionsof the tyre. When the vulcanization is complete, the tyre is removedfrom the vulcanization mould.

While the present invention has been specifically illustrated inconnection with a tyre, other cross-linked elastomeric manufacturedarticles that can be produced according to the invention may be, forexample, conveyor belts, driving belts or flexible tubes.

The present invention will be hereinafter further illustrated by someembodiments given by way of example only and thus not being restrictiveof same.

EXAMPLES 1-2

Preparation of the Elastomeric Compositions

The elastomeric compositions given in Table 1 (the amounts of thedifferent components are expressed in phr) were prepared as follows.

All ingredients except zinc oxide, the antioxidant, sulphur and theaccelerators, were mixed in an internal mixer (Pomini PL 1.6 model) forabout 5 minutes. As soon as the temperature of 145±5° was reached, theelastomeric composition was discharged. Then zinc oxide and theantioxidant were added and mixing was carried out in an internal mixer(Pomini PL 1.6 model) for about 4 minutes. As soon as the temperature of125±50 was reached, the elastomeric composition was discharged. Thensulphur and the accelerators were added and mixing was carried out in anopen mill mixer equipped with cylinders. TABLE 1 Example 1(*) 2 S-SBR 9090 BR 35 35 Silica 70 70 Titanium dioxide — 1.12 TESPT 5.6 5.6 Stearicacid 2 2 Aromatic oil 8 8 Microcrystalline wax 1 1 Zinc oxide 2.5 2.5Antioxidant 2 2 CBS 2 2 DPG 1.9 1.9 Sulphur 1.2 1.2(*)comparative.S-SBR: styrene/butadiene copolymer, obtained by solution polymerization,containing 25% by weight of styrene, mixed with 37.5 phr of oil (Buna ®5025 - Bayer);BR: cis-1,4-polybutadiene (Europrene ® BR 40 - EniChem Elastomeri);Silica: precipitated silica (Zeosil ® 1165 MP - Rhône-Poulenc);Titanium dioxide: purity: greater than 99%; surface area 8 m²/g; averagediameter of particles: comprised between 20 nm and 200 nm; (Kronos ®1002 - Kronos International);TESPT: bis(3-triethoxysilylpropyl)tetrasulfide (X50S comprising 50% ofcarbon black and 50% of silane from Degussa - the reported amountrelates to the silane amount);Antioxidant: N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine;CBS (accelerator): N-cyclohexyl-2-benzotiazyl-sulfenamide (Vulkacit ®CZ - Bayer);DPG (accelerator): N-N′-diphenylguanidine.

The Mooney viscosity ML(1+4) at 100° C. was measured, according to ISOstandard 289/1, on the non-crosslinked compositions obtained asdescribed above. The results obtained are given in Table 2.

Said elastomeric compositions were also submitted to a MDR rheometricanalysis using a MDR rheometer from Monsanto, the tests being run at151° C. for 60 minutes, with an oscillation frequency of 1.66 Hz (100oscillations per minute) and an oscillation amplitude of +0.5°. Thestatic mechanical properties according to ISO standard 37 as well ashardness in IRHD degrees at 23° C. according to ISO standard 48 weremeasured on samples of said elastomeric compositions cross-linked at151° C. for 30 minutes. The results obtained are given in Table 2.

Also given in Table 2 are the dynamic mechanical properties measuredusing an Instron dynamic device in the traction-compression modeaccording to the following methods. A test piece of the crosslinkedmaterial having a cylindrical form (length=25 mm; diameter=14 mm)compression-preloaded up to 10% longitudinal deformation with respect tothe initial length, and kept at the prefixed temperature (23° C. or 70°C.) for the whole duration of the test, was submitted to a dynamicsinusoidal strain with an amplitude ±3.33% with respect to the lengthunder pre-load, with a frequency of 100 Hz. The dynamic mechanicalproperties are expressed in terms of dynamic elastic modulus (E′) andtandelta (loss factor) values. As is known, the tandelta value iscalculated as a ratio between the viscous modulus (E″) and the elasticmodulus (E′), both of them being determined with the above dynamicmeasurements.

Also measured were the DIN abrasion values according to ISO standard4649, also given in Table 2, expressed as an index of a relativevolumetric loss with respect to the reference composition of Example 1(put to 100).

Finally, the amount of the reacted silane was measured. To this aim, aspecimen in the form of a sheet with a thickness of 1 mm of said notcross-linked elastomeric compositions having a weight of about 1 g, wasput into a Soxlet extractor with absolute ethanol for 24 hours so as toextract the unreacted silane therefrom. The extracted product wascooled, filtered and brought to volume with absolute ethanol. The amountof the extracted silane was determined by silica emission spectroscopy,using a plasma emission spectrometer SPECTRASPAN III model, by comparingthe intensity of the obtained signal with a calibration curve obtainedwith solutions having a known concentration of silane in ethanol. Theamount of the starting silane and the amount of the extracted silanebeing known, the amount of the reacted silane is given by the followingformula:${\%\quad{reacted}\quad{silane}} = {100 - \left\lbrack \frac{A}{B \times M} \right\rbrack}$wherein:

-   A=silane concentration in ppm, determined in the specimen brought to    volume in 100 ml of ethanol;-   B=percent by weight of silane added to the elastomeric composition;-   M=mass of the specimen in grams.

The obtained results are given in Table 2. TABLE 2 EXAMPLE 1(*) 2 Mooneyviscosity 80 81 ML (1 + 4) STATIC MECHANICAL PROPERTIES 100% Modulus(MPa) 2.09 2.06 300% Modulus (MPa) 9.93 9.47 Stress at break (MPa) 14.4014.35 300% Mod./100% Mod. 4.27 4.59 DYNAMIC MECHANICAL PROPERTIES E′(23° C.) (MPa) 8.12 8.36 E′ (70° C.) (MPa) 5.76 5.90 Tandelta (23° C.)0.273 0.270 Tandelta (70° C.) 0.140 0.130 RHEOMETRIC PROPERTIES MH (dNm) 21.1 20.9 t30 (min) 6.6 7.0 t90 (min) 8.0 8.1 IRHD Hardness (23° C.)69 68 IRHD Hardness (100° C.) 65 64 DIN abrasion (Index) 100 88 Reactedsilane (%) 87 92(*)comparative.From the experimental results given in Table 2, it is possible to noticethe following. Use of titanium dioxide in accordance with the presentinvention (Example 2) enables a stronger reinforcing effect to beobtained with respect to the comparative Example 1,# as proved by the value of the 300% modulus/100% modulus ratio. Inaddition the cross-linked manufactured article has improved hysteresisproperties, in particular lower tandelta values at 70° C. # (i.e. lessrolling resistance) and an improved abrasion resistance. Furthermore,the elastomeric composition in accordance with the present invention(Example 2) shows a higher reacted silane amount (%) as compared withthe reference composition (Example 1). # Said results show that titaniumdioxide is able to promote the reaction between silica and couplingagent and, consequently, to promote the interaction between silica andelastomeric polymer.

It should be also pointed out that the above effects were achievedwithout adversely affecting Mooney viscosity and vulcanisation kinetics.

1-25. (canceled)
 26. A tyre for a vehicle wheel, comprising: at leastone element of cross-linked elastomeric material; wherein the at leastone element comprises an elastomeric composition, comprising: at leastone diene elastomeric polymer; at least one reinforcing fillercomprising silica; at least one silica coupling agent comprising atleast one hydrolyzable silane group; and titanium dioxide; wherein aweight ratio of the at least one silica coupling agent to the titaniumdioxide is greater than or equal to 0.5:1.
 27. The tyre of claim 26,comprising: a carcass structure; a belt structure applied to the carcassstructure in a circumferentially external position relative to thecarcass structure, a tread band superimposed circumferentially on thebelt structure; a pair of sidewalls applied laterally on opposite sidesrelative to the carcass structure; wherein the carcass structurecomprises at least one carcass ply, wherein the carcass structurecomprises a substantially toroidal configuration, wherein oppositelateral edges of the carcass structure are associated with respectivebead wires, wherein each bead wire is enclosed in a respective bead,wherein the belt structure comprises at least one belt strip, andwherein the at least one element comprising an elastomeric compositionis the tread band.
 28. The tyre of claim 26, wherein the weight ratio ofthe at least one silica coupling agent to the titanium dioxide isgreater than or equal to 2:1 and less than or equal to 6:1.
 29. The tyreof claim 26, wherein the at least one diene elastomeric polymer isselected from unsaturated-chain elastomeric polymers or copolymershaving a glass transition temperature (T_(g)) lower than 20° C.
 30. Thetyre of claim 29, wherein the at least one diene elastomeric polymer isone or more of: cis-1,4-polyisoprene; 3,4-polyisoprene; polybutadiene;possibly halogenated isoprene/isobutene copolymers;1,3-butadiene/acrylonitrile copolymers; styrene/1,3-butadienecopolymers; styrene/isoprene/1,3-butadiene copolymers; andstyrene/1,3-butadiene/acrylonitrile copolymers.
 31. The tyre of claim26, wherein the elastomeric composition further comprises at least oneelastomeric polymer of at least one monoolefin with at least oneolefinic comonomer or derivatives thereof.
 32. The tyre of claim 26,wherein the elastomeric composition further comprises at least onethermoplastic polymer comprising a main hydrocarbon chain to whichhydrophilic groups are bonded.
 33. The tyre of claim 26, wherein the atleast one reinforcing filler comprises silica having a BET surface area,measured according to ISO Standard 5794/1, greater than or equal to 50m²/g and less than or equal to 500 m²/g.
 34. The tyre of claim 26,wherein the elastomeric composition comprises the at least onereinforcing filler in an amount greater than or equal to 0.1 phr andless than or equal to 120 phr.
 35. The tyre of claim 26, wherein the atleast one silica coupling agent further comprises at least one sulphuratom.
 36. The tyre of claim 26, wherein the at least one silica couplingagent is selected from compounds of formula:Z-Alk-S_(n)-Alk-Z wherein Z is selected from the following groups:—Si(R₁)₂(R₂), —Si(R₁)(R₂)₂, and —Si(R₂)₃; wherein R₁ is a C₁-C₄ alkylgroup, a cyclohexyl, or a phenyl group, wherein R₂ is a C₁-C₈ alkoxygroup or a C₅-C₈ cycloalkoxy group, wherein Alk is a divalenthydrocarbon group having from 1 to 18 carbon atoms, and wherein n is anumber greater than or equal to 2 and less than or equal to
 8. 37. Thetyre of claim 26, wherein the elastomeric composition comprises the atleast one silica coupling agent in an amount greater than or equal to 1phr and less than or equal to 15 phr.
 38. The tyre of claim 26, whereinthe titanium dioxide is selected from those having an NSA surface area,measured by surface absorption of nitrogen according to ISO Standard5794/1, greater than or equal to 5 m²/g and less than or equal to 200m²/g.
 39. The tyre of claim 26, wherein the titanium dioxide is selectedfrom those having an average particle diameter greater than or equal to10 nm and less than or equal to 400 nm.
 40. The tyre of claim 26,wherein the elastomeric composition comprises an amount of the titaniumdioxide greater than or equal to 0.2 phr and less than or equal to 5phr.
 41. An elastomeric composition, comprising: at least one dieneelastomeric polymer; at least one reinforcing filler comprising silica;at least one silica coupling agent comprising at least one hydrolyzablesilane group; and titanium dioxide; wherein a weight ratio of the atleast one silica coupling agent to the titanium dioxide is greater thanor equal to 0.5:1.
 42. The composition of claim 41, wherein the weightratio of the at least one silica coupling agent to the titanium dioxideis greater than or equal to 2:1 and less than or equal to 6:1.
 43. Thecomposition of claim 41, wherein the at least one diene elastomericpolymer is selected from unsaturated-chain elastomeric polymers orcopolymers having a glass transition temperature (T_(g)) lower than 20°C.
 44. The composition of claim 43, wherein the at least one dieneelastomeric polymer is one or more of: cis-1,4-polyisoprene;3,4-polyisoprene; polybutadiene; possibly halogenated isoprene/isobutenecopolymers; 1,3-butadiene/acrylonitrile copolymers;styrene/1,3-butadiene copolymers; styrene/isoprene/1,3-butadienecopolymers; and styrene/1,3-butadiene/acrylonitrile copolymers.
 45. Thecomposition of claim 41, further comprising at least one elastomericpolymer of at least one monoolefin with at least one olefinic comonomeror derivatives thereof.
 46. The composition of claim 41, furthercomprising at least one thermoplastic polymer comprising a mainhydrocarbon chain to which hydrophilic groups are bonded.
 47. Thecomposition of claim 41, wherein the at least one silica coupling agentcomprises silica having a BET surface area, measured according to ISOStandard 5794/1, greater than or equal to 50 m²/g and less than or equalto 500 m²/g.
 48. The composition of claim 41, wherein the elastomericcomposition comprises the at least one reinforcing filler in an amountgreater than or equal to 0.1 phr and less than or equal to 120 phr. 49.The composition of claim 41, wherein the at least one silica couplingagent further comprises at least one sulphur atom.
 50. The compositionof claim 41, wherein the at least one silica coupling agent is selectedfrom compounds of formula:Z-Alk-S_(n)-Alk-Z wherein Z is selected from the following groups:—Si(R₁)₂(R₂), —Si(R₁)(R₂)₂, and —Si(R₂)₃; wherein R₁ is a C₁-C₄ alkylgroup, a cyclohexyl, or a phenyl group, wherein R₂ is a C₁-C₈ alkoxygroup or a C₅-C₈ cycloalkoxy group, wherein Alk is a divalenthydrocarbon group having from 1 to 18 carbon atoms, and wherein n is anumber greater than or equal to 2 and less than or equal to
 8. 51. Thecomposition of claim 41, wherein the titanium dioxide is selected fromthose having an NSA surface area, measured by surface absorption ofnitrogen according to ISO Standard 5794/1, greater than or equal to 5m²/g and less than or equal to 200 m²/g.
 52. The composition of claim41, wherein the titanium dioxide is selected from those having anaverage particle diameter greater than or equal to 10 nm and less thanor equal to 400 nm.
 53. The composition of claim 41, wherein theelastomeric composition comprises an amount of the titanium dioxidegreater than or equal to 0.2 phr and less than or equal to 5 phr.
 54. Atread band for a vehicle wheel tyre, comprising: an elastomericcomposition, comprising: at least one diene elastomeric polymer; atleast one reinforcing filler comprising silica; at least one silicacoupling agent comprising at least one hydrolyzable silane group; andtitanium dioxide; wherein a weight ratio of the at least one silicacoupling agent to the titanium dioxide is greater than or equal to0.5:1.
 55. A cross-linked elastomeric manufactured article obtained bycross-linking an elastomeric composition, wherein the elastomericcomposition comprises: at least one diene elastomeric polymer; at leastone reinforcing filler comprising silica; at least one silica couplingagent comprising at least one hydrolyzable silane group; and titaniumdioxide; wherein a weight ratio of the at least one silica couplingagent to the titanium dioxide is greater than or equal to 0.5:1.